1. Field of the Invention
This invention relates to an optical coordinate input device and, more particularly, to a matrix driver for scanning, driving, and controlling individual diodes contained in a diode matrix composed of a plurality of light emitting diodes.
2. Description of the Prior Art
The optical coordinate input device comprises, for example, a light emitting element array. This array includes a plurality of light emitting diodes arranged in the form of a matrix wherein each light emitting diode is driven and caused to emit light when a row signal and a column signal pertinent thereto, serving as scanning signals, coincide in timing with each other. The light emitting diodes are driven by pulses, and the peak value of a current supplied to each diode during the scanning is made as large as some ten times the rated value during the static driving.
Examples of the foregoing type of optical coordinate input device are disclosed in U.S. Pat. Nos. 3,764,813; 3,775,560; and 3,860,754.
According to these patents, the row signals and the column signals are given each in the form of a pulse signal of square waveform. Therefore, if some malfunction occurs in a section for generating such pulse signals and a "high" level is preserved, only light emitting diodes located at row-column positions pertinent to the pulse signals kept at that level are caused to emit light continuously. As a result, the diodes would be destroyed due to continued energization, or the lifetime would be shortened.